Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, for example, light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The atomic structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed calculations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, that is, front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of semiconductor die on the surface of a semiconductor wafer. Each semiconductor die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual semiconductor die from the finished wafer and packaging the die to provide structural support and environmental isolation. The term “semiconductor die” as used herein refers to both the singular and plural form of the words, and accordingly can refer to both a single semiconductor device and multiple semiconductor devices.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller semiconductor die size can be achieved by improvements in the front-end process resulting in semiconductor die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
Back-end processing of semiconductor die includes a number of surface mount technologies (SMT) that are used to connect semiconductor die or integrated circuits to surfaces of substrates and PCBs without the use of through holes in the PCBs. Quad Flat Packages (QFP) use SMT that includes leads that extend from each of the four sides of the package, sometimes referred to as “gull wing leads.” QFP leads provide electrical Input/Output (I/O) interconnection between the semiconductor die within the package and the PCB or substrate to which the QFP is mounted. Other SMT packages are made without leads and are commonly referred to flat no lead packages. Examples of flat no lead packages are Quad-flat no leads packages (QFNs) and dual-flat no lead (DFN) packages. QFN packages conventionally include a semiconductor die connected by wirebonds to a leadframe that is used for package I/O interconnection.
Both front-end manufacturing and back-end manufacturing can include processes or steps in which material is removed from a semiconductor device or semiconductor substrate, such as removal of undesired portions of a conductive layer, such as a seed layer or, removal of another undesired material, such as all or part of a photosensitive or photoresist material. Conventionally, removal of undesired material has been achieved with laser ablation or etching. Etching of undesired material has been conventionally performed in a bath or by spinning in a bowl.
Application of the etching solution to the material to be removed has conventionally been achieved by immersing the material to be removed, together with the wafer or panel on which the material has been formed, into a bath of the etching solution contained within a large tub or vat. The etching solution in the bath is conventionally contained within the bath, so as to prevent leakage and waste of the etching solution and, in the case of some submersion systems, inclusion of rolling seals where the wafer or panel enters and exits the bath can also be included. The rolling seals apply pressure to the panel, wafer, or other object being inserted into the bath. Structural supports, such as dummy metal features, are conventionally added or included on the wafer or panel to prevent pressure from the rolling seals breaking or damaging the wafer or wafer structures as the wafer and wafer structure pass through each rolling seal.
An etch process using bowls and spinning the wafer has also been utilized in some cases for processing semiconductor wafers. The bowl method for etching semiconductor wafers is significantly more expensive given process times, which can exceed 10 minutes and can require substantial capital equipment investment for multiple bowls and related automation. The bowl method does in some cases have the process control and maintenance advantage of single use chemical solutions, eliminating the maintenance of recirculating baths associated with submersion methods.